What is delirium?

Delirium happens when a person has sudden confusion or a sudden change in mental status. The person may have trouble paying attention or thinking clearly. They may act disoriented or distracted.

Delirium is more severe than having a “senior moment” — the minor problems people have with memory and understanding as they get older. It requires treatment and often hospitalization.

Is delirium a disease?

No, delirium is not a disease. It’s a changed mental state.

Is delirium the same as dementia?

Delirium and dementia (which includes conditions such as Alzheimer’s disease) have some similarities, but they are not the same.

  • Delirium mostly affects a person’s attention. Dementia affects memory.
  • Delirium is a temporary state that begins suddenly. Dementia is chronic (long-term) confusion that usually begins gradually and worsens over time.

However, someone can have both delirium and dementia. Seek care quickly if a person, especially one with dementia, begins to show symptoms of delirium.

What are the types of delirium?

The two types of delirium are:

  • Hyperactive delirium: The person becomes overactive (agitated or restless).
  • Hypoactive delirium: The person is underactive (sleepy and slow to respond).

Hypoactive delirium is more common, occurring in up to 75% of people with delirium. But many people, including healthcare providers, may incorrectly assume the person is depressed.

People can experience both types of delirium together. They can be extremely alert one minute and drowsy the next.

Who is at risk for developing delirium?

Delirium happens more often in older people and hospitalized patients. “Hospital delirium” can affect 10% to 30% of those patients.

People in these high-risk populations may develop delirium:

  • People who have had surgery.
  • 80% of people who are at the end of life.
  • 70% of people in intensive care units (ICUs).
  • 60% of people over age 75 in nursing homes.
  • 30% to 40% of people who have human immunodeficiency virus (HIV).
  • 25% of people with cancer.

People may also be at higher risk for developing delirium if they:

  • Are on dialysis.
  • Can’t move because of catheters or restraints.
  • Don’t get enough sleep or are dehydrated.
  • Have burns.
  • Have more than one illness, have a chronic condition or take multiple medications.
  • Have Parkinson’s disease, chronic liver disease or had a stroke.
  • Have trouble hearing or seeing.
  • Suddenly stop using alcohol or drugs (withdrawal).

How common is delirium?

Because delirium is temporary, it’s hard to know exactly how many people develop it. Researchers estimate that hospital delirium affects 15% to 50% of people.

What are the causes of delirium?

In some cases, providers can’t find a cause of delirium.

Known causes of delirium include:

  • Alcohol or illegal drug toxicity, overdose or withdrawal.
  • Overwhelming reaction to infections such as pneumonia, sepsis and urinary tract infections.
  • Changes in the environment.
  • Dehydration.
  • Medications, such as those with anticholinergic effects (including antihistamines), psychoactive drugs and opioids.
  • Hormonal issues (such as hyperthyroidism or hypothyroidism).
  • Hospitalization or surgery.
  • Kidney or liver injury or failure.
  • Lack of oxygen to your tissues.
  • Lack of sleep.
  • Pain.

What are the symptoms of delirium?

The different types of delirium produce different symptoms. Symptoms tend to start suddenly and get worse over the next few hours or days. A person with delirium may act like they’re intoxicated. The main symptom is being unable to pay attention. Symptoms tend to become worse in the evening, which is known as sundowning.

Symptoms of hyperactive delirium include:

  • Acting disoriented.
  • Anxiety.
  • Hallucinations.
  • Rambling.
  • Rapid changes in emotion.
  • Restlessness.
  • Trouble concentrating.

Symptoms of hypoactive delirium include:

  • Apathy.
  • Decreased responsiveness.
  • Flat affect.
  • Laziness.
  • Withdrawal.

Last reviewed by a Cleveland Clinic medical professional on 09/16/2020.


  • HealthinAging.org. Delirium. Accessed 9/18/2020.
  • Merck Manual. Delirium. Accessed 9/18/2020.
  • U.S. National Library of Medicine. Delirium. Accessed 9/18/2020.

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